In the nuclear power plant, a high-temperature and high-pressure water is used, and a high reliability is demanded. Accordingly, in order to prevent an aged deterioration phenomenon, particularly a stress corrosion crack, the nuclear power plant is manufactured by a method which suppresses a generation of a residual stress due to a working strain or a tensile stress likely causing the stress corrosion crack.
Patent document 1 discloses a method of setting a residual stress close to a backside of groove bottom surface to a compression stress or a small tensile stress, by a narrow groove welding method for a nuclear structure with a root face. Particularly, it relates to the narrow groove welding method and the welding structure with the root face, and a welding apparatus thereof, and the patent document 1 discloses a method of improving a residual stress of a groove bottom surface to a compression, characterized by employing an arc welding method as a welding method, and is provided with a first layer welding step of forming a weld bead in a backside surface of the groove bottom portion, a step of deposition welding in a first heat input range to a specific deposited bead height after the first layer welding step, and a step of welding a remaining portion by a second heat input range.
Patent document 2 relates to a method of welding a extreme thick plate for a nuclear plant, and discloses a joint shape having a root face welded by a low heat input and a remaining groove portion deposition welded by an conventional arc welding. Particularly, it describes a method of welding an extreme thick steel with a possible lower range of heat input and a remaining portion is welded by an arc welding.
Patent documents 3 and 4 disclose a welding method of deposition welding a narrow groove by using a laser welding and a welding groove shape. The patent document 3 discloses a narrow groove laser welding method of setting a welded portion to a narrow groove width, irradiating a laser beam into the narrow groove while feeding a filler wire, melting the filler wire by the laser beam, and deposition build-up welding.
The patent document 4 discloses a welding method of setting a narrow groove in butted portions of weld subject members and setting a curvature to a bottom portion of the groove, setting a root face of 1 mm to 5 mm to the butted portions, and setting a ratio of a depth of weld penetration with respect to a width of weld to a predetermined range (which is equal to or more than 1 and equal to or less than 1.4), as a method of welding metals to each other by using a laser beam and a method of manufacturing a liquefied gas tank.
Patent Document 1: JP-A-2007-21516
Patent Document 2: JP-A-58-151988
Patent Document 3: JP-A-9-201687
Patent Document 4: JP-A-2007-190568